This invention relates to apparatus for rotating the work platform on a boom type lift.
Boom type lifts are well known. Such lifts normally have a work platform attached to the end of a boom which may be either fixed in length or extensible. The work platform is normally fixed to the end of the boom with respect to rotation, but may utilize a vertically pivotal, self-leveling connection, so as to maintain the work platform in a position with a horizontal floor for comfort and safety of the workmen.
A device to permit the work platform to be rotated are illustrated in U.S. Pat. No. 3,605,941, issued Sept. 20, 1971, which provides for manual rotation of the work platform. An electrically driven chain drive platform rotation apparatus is shown in U.S. Pat. No. 3,709,322, issued Jan. 9, 1973. In U.S. Pat. No. 3,841,436, issued Oct. 15, 1974, a rotary hydraulic motor is utilized to rotate the work platform. However, none of these devices has received widespread acceptance in the industry, due to their particular constructional features, such as manual operation, additional expense of components involved, and the like.
According to the present invention, apparatus for the 180.degree. rotation of a work platform on a boom lift includes a pivot pin which is attached to the end of the boom so that the pin is disposed substantially vertically. A work platform frame is pivotally connected to the pin. An idler bracket is also pivotally mounted on the pin and has a first idler arm and a second idler arm, each of which extend outwardly horizontally from the pin and which are offset, one with respect to the other, at an angle of from about 90.degree. to about 120.degree.. A first hydraulic piston and cylinder assembly is pivotally connected between the first idler arm and the work platform frame so that application of hydraulic fluid under pressure to one side of the piston will rotate the frame in a clockwise direction and application of hydraulic fluid under pressure to the opposite side of the piston will rotate the frame in a counterclockwise direction. The total range of movement of the frame with respect to the action of the first hydraulic assembly is approximately 90.degree.. A second hydraulic assembly is pivotally connected between the second idler arm and the boom attaching means so that the application of hydraulic fluid to one side of the second hydraulic piston rotates the bracket in a clockwise direction with respect to the boom and the application of hydraulic fluid under pressure to the other side of the second hydraulic piston rotates the bracket in the opposite direction. Hydraulic fluid under pressure from the hydraulic fluid source is selectively applied to the first and second hydraulic pistons so as to provide a cumulative rotational movement. That is, the clockwise rotation of the frame in response to the first hydraulic assembly is accompanied by clockwise rotation of the bracket in response to the second hydraulic assembly. By such a complementary hydraulic arrangement, rotation of the work platform through an arc of about 180.degree. is achieved, whereas each cylinder, alone, could only rotate the work platform through an arc of about 90.degree..